Things started off fine and well, until the host of the Mojo In The Morning show decided to compare Bieber to another well-known pop singer.

"I hope you take this as a compliment," said Mojo. "When I heard 'Boyfriend' for the very first time, I thought it was Justin Timberlake's single."

"Saying I sound like someone else is not really a compliment," Bieber retorted.

That wasn't the only thing that got his goat. Mojo went on to ask about the singer's friendship with teen heartthrob band One Direction, and that led to the straw that broke the Biebs' back.

After Bieber noted that the One Direction lads were "good kids," the host blasted him with the following question: "Do you worry about Harry around your mom, since he likes older women?" (One Direction's Harry Styles has reportedly dated several women in their 30s.)

"Do I wonder...what?" answered a confounded-sounding Bieber.

After the question was repeated, Bieber snapped back in a chilly tone, "I think you should worry about me around your mom, bro."

In the following clip, Mojo explains the entire scenario, noting that Bieber's handlers first called back and blamed bad cell phone reception for the dropped call...but then later admitted the singer was upset by the question.

What do you think? Did the radio host cross a line? To us, it seems fairly silly stuff...but then again, it's never wise to bring anyone's mom into these sorts of discussions. Right?